KR20110048525A - Carbon Nanotube-Reinforced Nanocomposites - Google Patents

Abstract

Carbon nanotubes (CNTs) are so long that such carbon nanotubes cannot penetrate between carbon fibers during the prepreg fabrication process, which is shortened to prevent leakage by the carbon fibers. This significantly improves the mechanical properties (flexural strength and flexural modulus) compared to pure epoxy.

Description

Carbon Nanotube-Reinforced Nanocomposites {CARBON NANOTUBE-REINFORCED NANOCOMPOSITES}

This application is partly filed in US Patent Application No. 11 / 757,272, which claims priority to US Provisional Application Nos. 60 / 819,319 and 60 / 810,394, all of which are incorporated herein by reference. This application is partly filed in US patent application Ser. No. 11 / 693,454, which claims priority to US Provisional Application Nos. 60 / 788,234 and 60 / 810,394, all of which are incorporated herein by reference. This application is partly filed in US Patent Application No. 11 / 695,877, which claims priority to US Provisional Application Nos. 60 / 789,300 and 60 / 810,394, all of which are incorporated herein by reference.

Since its first observation in 1991, carbon nanotubes (CNTs) have been the center of considerable research [S. Iijima, "Helical microtubules fo graphitic carbon", Nature 354, 56 (1991). Many researchers have reported the remarkable physical and mechanical properties of this new type of carbon. CNTs typically have diameters of 0.5-1.5 nm for single wall CNTs (SWNTs), 1-3 nm for double wall CNTs (DWNTs) and 5 to 100 nm for multiwall CNTs (MWNTs). From the unique electronic properties and higher mechanical properties of materials with higher thermal conductivity, to stiffness, strength and elasticity than diamond, CNT offers great opportunities for the development of basic new material systems. In particular, the development of CNT-reinforced composite materials attracted interest due to the low mechanical density (1-2.0 g / cm ³ ) and the special mechanical properties of CNTs (tensile strength of E> 1.0 TPa and 50 GPa) [Eric W. Wong Paul E. Sheehan, Charles M. Lieber, "Nanobeam Mechnics: Elasticity, Strength, and Toughness of Nanorods and Nonotubes", Science 277, 1971 (1997). CNT is the strongest material known on earth. Compared with MWNTs, SWNTs and DWNTs are more promising as reinforcing materials for composites because of their high surface area and high aspect ratio. Table 1 shows the surface area and aspect ratio of SWNTs, DWNTs and MWNTs.

TABLE 1

The problem is that when CNTs are grown, they are usually quite long (a few microns to 100 μm or more), which makes CNTs difficult to penetrate the matrix in fiber reinforced plastics (FRP) because the distance between the nearest fibers is too short. For example, in the case of unidirectional carbon fibers or fiber reinforced epoxy composites, the content of carbon fibers is such that the gap between the nearest carbon fibers is approximately 1 micron (carbon fibers have a diameter of 7-8 μm and approximately 1.75 − Approximately 80% by volume), with a density of 1.80 g / cm 3 and assuming that the epoxy matrix has a density of 1.2 g / cm 3. The same is true for the glass fibers and other types of fibers used to make the composites. CNTs can reinforce polymer resins to improve mechanical properties such as strength and modulus, but they cannot reinforce FRP because they are filtered out by fibers during FRP manufacture.

1 illustrates a method of manufacturing a nanocomposite according to an embodiment of the present invention.
2 shows an SEM digital image of MWNTs.
3A-3C show SEM digital images of the fracture surfaces of each of the MWNT-reinforced epoxy, DWNT-reinforced epoxy, and SWNT-reinforced epoxy.
4A shows a SEM digital image of the fracture surface of DWNT-reinforced CFRP, showing no DWNT penetration between the carbon fibers.
4B shows a SEM digital image of the fracture surface of the DWNT-reinforced CFRP, showing leaking out of the end layer of the prepreg.
5A-5C show SEM digital images of shortened MWNTs, DWNTs, and SWNTs, respectively.
6A-6C show SEM digital images of fracture surfaces of MWNT-reinforced CFRP, DWNT-reinforced CFRP, and SWNT-reinforced CFRP, respectively.

CNTs as short as or shorter than 2 μm can penetrate between fibers, thereby significantly improving the mechanical properties of the FRP.

In one embodiment of the invention, detailed examples of this embodiment are provided in an effort to better illustrate the invention.

Epoxy, SWNT , DWNT , MWNT , And hardeners

Epoxy resin (bisphenol-A) was obtained from Arisawa Inc., Japan. Curing agent (dicyandiamide) was obtained from the same company, which was used to cure epoxy nanocomposites. SWNTs, DWNTs and MWNTs were obtained from Nanocyl, Inc., Belgium. CNTs can be purified to a carbon content of greater than 90%. However, native CNTs or CNTs functionalized by functional groups such as carboxyl and amino-functional groups can also be used. The length of the CNTs may be approximately 5-20 μm. 2 shows a digital image of the SEM of the MWNT. Except for epoxy, other thermosetting materials such as polyimide, phenolic resins, cyanate esters, and bismaleimide or thermoplastics such as nylon can also be used.

1 shows a schematic diagram of a process flow for producing an epoxy / CNT nanocomposite according to one embodiment of the invention. All components can be dried for 16 hours in a 70 ° C. vacuum oven to remove moisture. The loading of CNTs for each of the resins can be 1.0 weight percent. The CNTs are placed in acetone (101) and dispersed by micro-fluidic device in step 102 (commercially available from Microfluidics Co., Model No. Y110). Micro-fluidic devices utilize high pressure streams that collide at very high speeds in precisely defined micro-sized channels. Its combined force of shear and impact forces acts on the product to produce a uniform dispersion. CNT / acetone is then formed as a gel in which CNTs are well dispersed in acetone solvent (103). However, other methods may also be used, such as an ultrasonic process or a high shear mixing process. Surfactants can also be used to disperse the CNTs in solution. The epoxy is then added to the CNT / acetone in step 104 to produce an epoxy / CNT / acetone solution (105), which is subjected to an ultrasonic process for 1 hour in a bath at 70 ° C. to produce an epoxy / CNT / acetone suspension. (107). The CNTs are further dispersed in epoxy using a stirrer mixing process at a rate of 1,400 cycles / minute for 30 minutes at 70 ° C. in step 108 to produce an epoxy / CNT / acetone gel (109). The curing agent is subsequently added to the epoxy / CNT / acetone gel 109 in step 110 at a rate of 4.5% by weight and then stirred at 70 ° C. for 1 hour. The resulting gel 111 may then be degassed for 48 hours in a vacuum oven at 70 ° C. in step 112. This material 113 may then be cured at 160 ° C. for 2 hours. To test the material 113, it can then be poured into a Teflon mold such that the mechanical properties (flexural strength and flexural modulus) of the specimen are characterized after the polishing process 115.

After degassing at 70 ° C. for 48 hours, the resin (epoxy / CNT / curing agent) can also be used to prepare FRP using a hot-melt process. Carbon fibers (available from Toray Industries, Inc., model number T700-12k) can be used for prepreg production. "Prepreg" (or "pre-preg") is a term known in the art for "pre-impregnated" composite fibers. These may have a weave form or may be unidirectional. These contain a certain amount of matrix material used to bond these together and to other components during manufacture. The prepreg can be stored in a cooled zone because activation is most commonly carried out by heat. Accordingly, composite structure buildup of the prepreg will most likely require an oven or autoclave for curing.

The CNT-reinforced epoxy resin is first coated on a release paper. The prepreg is then obtained by impregnating unidirectional carbon fibers with a thin film of CNT-reinforced epoxy resin. The volume of carbon fiber was adjusted to 60%. The prepreg has an area weight of 180 g / m 2.

Mechanical Properties of Nanocomposites

Table 2 shows the mechanical properties (flexural strength and flexural modulus) of CNT-reinforced epoxy with reinforcement of unidirectional carbon fibers. This table shows, in the resin form, a significant improvement in mechanical properties compared to pure epoxy (flexural strength is more than 30% improvement, and flexural modulus is at least 10% improvement). However, in the form of carbon fiber reinforced polymer (CFRP), the properties of both did not improve in the case of CNT-reinforced CFRP compared to pure epoxy CFRP.

TABLE 2

Scanning electron microscopy (SEM) can be used to check the dispersion of CNTs in both resin and CFRP samples. In the resin form, all CNT-reinforced epoxy samples showed very good dispersion of CNTs (see FIGS. 3A-3C). However, CNTs were leaked into the end layer of the prepreg by unidirectional carbon fibers (see FIGS. 4A and 4B for DWNT-reinforced epoxy CFRP). This is because the gap for the nearest carbon fiber is only approximately 1 μm, so the CNTs are too long such that they cannot penetrate between the carbon fibers. This is why the reinforcement of CNTs in the resin does not migrate to CFRP.

CNT Shortening, and epoxy resin and CFRP Reinforcement

Since the CNTs are so long that these cannot be penetrated between the carbon fibers during the prepreg manufacturing process, the CNTs must be shortened to prevent leakage by the carbon fibers. MWNT, DWNT, and SWNT can be mixed with a concentrated acid mixture (HNO ₃ : H ₂ SO ₄ = 3: 1) and stirred at 120 ° C. for 4 hours. CNTs are filtered using filter paper (polycarbonate filter paper with a 2 micron opening for filtering acid). The CNTs were then washed 4 to 5 times with ionized water and dried at 50 ° C. or higher in vacuo for 12 hours. 5A-5C show SEM images of MWNTs, DWNTs, and SWNTs each shortened to a length of less than 2 μm.

Table 3 shows the mechanical properties (flexural strength and flexural modulus) of shortened CNT-reinforced epoxy with reinforcement of unidirectional carbon fibers. Table 3 shows a significant improvement in the mechanical properties compared to pure epoxy in the resin form (an improvement in flexural strength of at least 30% and an improvement in flexural modulus of at least 10%), which are in line with the above mentioned long CNT-reinforced epoxy resins. similar. In the CFRP form, the properties of both were improved compared to pure epoxy CFRP. For example, the flexural strength of SWNT-reinforced CFRP was improved by 17% compared to pure epoxy CFRP.

TABLE 3

Scanning electron microscopy (SEM) can be used to check the dispersion of CNTs in CFRP samples. As shown in FIGS. 6A-6C, shortened MWNTs, DWNTs, and SWNTs are penetrated between carbon fibers and well dispersed.

Claims (7)

A composite material comprising carbon nanotubes, polymers and carbon fibers, wherein the average length of carbon nanotubes is less than 2 μm. The composite material of claim 1, wherein the polymer is a thermoset or thermoplastic. The composite material of claim 2, wherein the thermosetting material is selected from the group consisting of polyimide, phenolics, cyanate esters, and bismaleimide. The composite material of claim 1, wherein the carbon nanotubes are not functionalized. The composite material of claim 1, wherein the carbon nanotubes are functionalized with carboxyl functional groups or amine functional groups. The composite material of claim 1, wherein the carbon nanotubes are functionalized with amine functional groups. The composite material of claim 1, wherein the carbon fibers are unidirectional carbon fibers.

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